For years chefs and cooks alike have been faced with the dilemma of determining the doneness of food, which is the condition of being cooked to the desired degree. For example, the desired degree of cooked meat is rare, medium or well done. There are many factors affecting how quickly meat cooks, such as temperature, thickness, percentage of fat, and the presence or absence of bone. Similar internal variations can be found in all foods, so for these reasons time and temperature cooking charts are not accurate.
Due to this problem chefs have adopted other means to determine when to remove food from heat to acquire the desired doneness. Many times they will use a “cake tester” which consists of a thin metal rod with a small plastic molded finger grip. The chef inserts a cake tester into the food to feel the texture and then places the metal rod of the tester on his/her lip or other part of their body to check the temperature in relationship to their body temperature. As an example, if meat is pierced with a metal rod and the chef touches the rod to his lip and the rod is cooler than the chef's lip, he knows that the meat is rare. The cake tester, however, has shortcomings. The rod is made of a metal that conducts heat very slowly, the rod is often subject to bending, and there is no convenient place for chefs to place it in their jacket where it is sanitary and where they can easily and quickly acquire it, no matter where they are in the kitchen.
Cake testers are designed to test cakes, not other foods like steak, fish, potatoes, etc., so they are not constructed of a durable metal that conducts or transmits heat quickly; nor are they made to resist bending that might occur when inserting the probe into food. There is also no sanitary means for a chef to carry a cake tester or any other metal rod in a convenient place that protects it from contamination and prevents it from bending while being carried.
Cake testers or other metal rods or probes that a chef might use are constantly falling out of pockets and getting lost. They can be difficult to retrieve from a pocket. As mentioned, the metal used in all existing probes is a poor conductor of heat.